High-frequency signaling



March 24, 1931. I R. EiCORAM 1,797,284

HIGH FREQUENCY SIGNALING Filed Nov. 24, 1925 m I &

Ex l

' /nven7ar Roy E 60ram Patented Mar. 24, 1931 UNITED STATES PATENT OFFICE ROY E. COBAI, OF NEWARK, NEW JERSEY, ASSIGNOB TO WESTERN" ELECTRIC CO]!- PANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK Y men-rnnounncy sronarme Application filed November 24, 1928. Serial No. 676,842.

This invention relates to a system of high frequency signaling and particularly to methods of multiplex two-way radio signaling.

An object of the invention is to provide,

5 in a multiplex two-way radio system, for the exact correspondence in frequency of the carrier waves of various oppositely directed channels and for the maintenance of correct spacing between channels similarly directed.

Specific objects of the invention are: to increase the effectiveness of two-way radio signal transmission using the same carrier and a single antenna for both the transmitted and received waves corresponding to each carrier radio signaling system of the above type in which the locally produced wave required for reception is derived from energy transmitted from the opposite station in such manner as to make interception by an unauthorized receiver diflicult; and to provide a system characterized as above further characterized'by economic utilization of energy, simplicity of circuit, and eflicient wave length utilization.

' These objects; together with other objects more fully hereinafter appearing, are partially realized in a radio system in which a single signal side band is transmitted in each direction, that is, in which the carrier and one side band is suppressed. Such a system is inherently more efficient, as requiring'the transmission of less energy, than one in which'both side bands are transmitted either withor without the carrier.

It is expedient to use a plural modulation method for producing the single signal side band in order that'the necessary selecting and separating operations may be performed at a relatively low carrier frequency instead of at a radio frequency. Double modulation with the suppression of oneside band after each stage is accordingly included in the operation of thepresent system. Besides the advantage of a. double modulation transmitting system stated above, it furthermakes possible multiplex transmission by the method of modulating each of a plurality of low frequency carrier waves with a signal and using the selected side bands of the modtwo-way channel; to provide a suppressed ulated products jointly to modulate a radio frequency carrier.

A multiplex system of closely adjacent frequency channels, like that proposed, would ordlnarlly require a multiple demodulation method in order to effect separation of the spacing to avoid interference .and'singing even if a common antenna is used as is contemplated by the invention. Specifically, it is proposed to use a single frequency setting source for the low frequency carriers of all of the multiplex channels at each station for both transmitting and receiving, the carrier frequencies being produced by harmonic generation, and also a single radio carrier source fortransmitting and receiving the multiplex waves at each station. a

To insure a frequency stability in the system as a whole, a system of control of the various carrier frequencies must be used. To this end, control frequencies, derived from the carrier frequencies at one of the stations, hereinafter called the master station, are sent to the other station hereinafter called the controlled station, to fix the carrier frequen- 'cies at the controlled station. The control radio carrier frequency wave is generated by a source at the master station. A multiple of this frequency is used as the radio carrier frequency. The control radio carrier frequency is transmitted from and received at separate antennae structures selective to necessar ponents from whichby harmonic regeneration the various carrier waves may be produced. The output circuit of the demodulator may be considered as the source for the carrier frequencies at the controlled station. Except for the dilference in character of the respective carrier sources at the two stations and the special circuits at each station which are necessary on account thereof, the two stations are identical.

The invention will be more fully understood by' reference to the figures of the accompanying drawing.

Fig. 1 discloses the circuits at the master station.

Fig. 2 discloses the control circuits at the controlled station.

In the drawing, the elements will be identified by reference letters which are suggestive of their functions, different elements having similar fimctions being distinguished by the use of different subscrlpts.

Referrin to Fig. 1, the circuits L, M TF M, T a and AN to ether comprise the combination 0% elements whereby signals rom low frequency line L are carried through a sequence of operations resulting finally in radiation from antenna AN as a modulated signal side bandof a doubly modulated wave. The circuitsAN,RF,D,RF ,D and L together correspondingly comprise the necessa elements whereby a modulated side band 0 a doubly modulated wave is received by antenna AN and carried through a sequence of operations finally resulting in the production of the signal wave in L These two groups of elements make up the terminal circuits of a complete two-way radio'signal channel. The lines L and L may be joined in a common line connected to, for example, atelephone subscribers substation. These circuits, in general, resemble thevcorresponding plural modulation and demodulation circuits of U. S. patent to Espenschied No. 1,447,204, issued March 6, 1923, to which reference is made for additional disclosure.

Specifically, device M is a modulator wherein low frequency carrier current from circuit 1 is modulated b the signal with attendant suppression of t e unmodulated carrier, such as is disclosed indetail in U. S. patent to Carson 1,343,306, issued June 15, 1920. One side band is eliminated by band pass filter TF which may be of the type disclosed in U. S. patent to Campbell 1,227,113, issued May 22, 1917. Circuit 1 is supplied with waves from source G through harmonic producer H. Source G produces a funda:

I mental frequency current, the harmonics derived from it by device H being usedto supply the low frequency carrier for the various transmittin and receiving channels at one station 'of t e multiplex system and, as will subsequently appear, determine the corresponding carrier frequencies at the controlled station. This source may be of any type such as, for example, a vacuum tube oscillator. The harmonic producer H may be, for example, of the distorting vacuum tube type disclosed in U. S. patent to Kendall, Serial No. 1,446,752, issued February 27, 1923. t

The resultant modulated side band is impressed on the modulator M which may be similar to modulator M and in which the side band from filter TF is used to modulate the radio carrier current from circuit 2. Circuit 2 is supplied with waves from source G and harmonic producer H An harmonic wave may be used but it is pre erable to use one of a small order on account of the usually greater energy content therein,

as compared with the higher harmonic. The

reason for usin a harmonic, instead of the. fundamental o the wave from source G will appear later. Devices G and H may be of the same types as the functionally similardevices G and H. Filter TF may be identical in type with TF It functions to eliminate one of the radio carrier side bands of the doubly modulated wave resulting from the finalmodulating operation. The selected side band is 'radiated by antenna AN which may be tuned to the radio carrier frequency.

Other transmission channels corresponding to the one just described may also be connected in common to the high frequency modulator M. The circuitM TF illustrates diagrammatically one of such channels, the functions of the elements being similar to those correspondinglylettered in the channel above described. The low frequency carrier for that channel is similarly derived from source G and harmonic producer H, a different harmonic, however, being used. The transmitted wave of each channel may be considered first as a single radio carrier side band of a doubly modulated wave in which a single side band is retained after the first stage of modulation, or second, as a single side band of a. signal modulated carrier wave in which the carrier is made up of the sum of a low fr uency and a radio frequency carrier wave. gn account 11! of the multiplex feature which requires double demodulation, involving the first conception, unless a plurality of radio frequency carrier frequencies are supplied, it is more convenient to use the first conception and it will be so-used in the remaining portion of this specification. Accordingly, in the claims such expressions as single side band of a doubly modulated wave or single side band where a doubly modulated wave is otherwise specified, are intended to define a doubly modulated wave having onl one of the possible four signal bearing si e bands.

In certain cases it may be expedient to retain both of the low frequency sidebunds, but only & 1,797,284-

one of the side bands of the radio carrie It will be understood, in the claims, that the expression sin le radio carrier side band, or the like, de nes a single side band of a wave resulting from the modulation of a radio carrier by a low frequency carrier wave, whether the low frequency carrier carries one, two, or no side bands.

A single radio side band of a doubly modulated wave similarly transmitted from the opposite station is received by antenna AN. This wave has the same radio carrier frequency as the outgoing wave but the opposite radio carrier side band, antenna AN being tuned broadly enough to receive both side bands. This side band is selected by band pass filter RF and transmitted to the demodulation circuits to be described. The coincidence of radio carrier frequencies and the use of different side bands thereof together insure efficient use of the same antenna with avoidance of singing.

The remaining portion of the receiving circuit has the same types of elements, and having the same functions although in the inverse order, as the corresponding elements in the transmitting circuit, and accordingly will not be described except as to function. The circuit operates as follows :The single radio carrier side band of the doubly modulated wave is demodulated by device D and selected by filter RF the radio carrier being supplied from circuit 2, demodulation being accompanied by suppression of the carrier. Since a single side bandis retained after the first stage of modulation at the opposite station, the demodulated product is one side band of a signal modulated low frequency carrier wave. This side band is demodulated in the second stage demodulator D to yield the signal. In this stage of demodulation as in the other, the carrier is supplied from the local transmitting source since the low, as well as the radio. carrier frequencies for each two-way channel are made the same for opposite directions of transmission. As in the first stage of demodulation, the carrier is suppressed by the use of the balanced arrangement of tubes. Although not essential, this feature as applied to either or both stages of demodulation conduces materially to the efiicient functioning of the system.

Although the suppression of the low frequency carrier or of one low frequency carrier side band. or both of these components, in the transmitting circuits has advantages, in the way of eliminating all but the essential frequency components with attendant greater insurance of reception without interference,

and of conservation of frequency range and of energy, it is pointed out that the elimination of one side band has the further advantage that if different low frequency side bands of the same low frequency carrier are transmitted in two directions, an impedance to different radio carrier side bands. As in the case of the radio carrier, this makes economic use of energy and of telephone plant possible by the use of the same low fre uency carrier for both of the two directions 0 transmission without attendant sacrifice of receiving efiiciency.

D and RF designate elements of a second receiving channel designed to cooperate with the transmittin channel M TF channelreceives lts carrier current by derivation from source G in the same manner as in the case of the receiver channel disclosed in detail, a different harmonic being used. The elements having similar labels are similar in structure and function as those in the receiving channel described in detail. The additional two-way channel comprising this receiver channel and the corresponding transmitting channel M TF may, and in practice would, be duplicated by other twoway channels similar to those described and .similarly related to the system as a whole.

The use of a single side band of a double modulated wave in each transmission channel of such a multiplex system results in the maximum economy of requency range, that is, it

makes possible the use of a maximum number of transmissions in a given frequency range.

Practical conditions of operation may require elements which, although they have the same' essential functions as those described, may be materially different in structure. Other elements may also be added. In particular, amplifiers may be required in various places. These various changes may be incorporated in the system without detriment to its function as a whole and without departing in any way from the essential novel principles of this invention.

In review the system as so far described comprises a combination of elements for multiplex two-way signaling, having the features of (1) the use of a single antenna; (2) the smallest frequency range in each transmission channel possible for intelligible transmission; (3) maximum economy of power used for transmission; (4) a transmitting and receiving arrangement which makes possible the closest crowding of channels in the system as a whole without interferences; and (5) an arrangement of frequencies which necessitates the use of a minimum-number of local generating sources.

' These various features, or certain of them,

are dependent upon the accurate synchronization of the low and carrier frequencies generated by the respective carrier sources at the two stations.

In a complete two-way system, one station, like that disclosed in Fig. 1, is the master station and embodies means'for determining the carrier frequencies for the whole system. At

This

this station the carrier sources are accordingly self-contained enerators. A The corre-.

sponding sources at t e other station are circuits carrying currents derived from the auxiliary antenna AN}. This control wave is a sub-harmonic of the radio carrier frequency at the master station and is accordingly capable, by harmonic generation, of supplying an equivalent radio carrier at the controlled station. Since the control frequency wave is widely different from the radio carrier fr uency wave, it can not readily be intercepte by an unauthorized person, who would ordinarily be equipped to IBCGIVQ only the message carrier wave.

A control wave for the low frequency carrier is transmitted from source G as a modulation of the radio carrier control wave. Modulation occurs in modulator M,. may be of any conventional type, not necessarily employing a vacuum tube, provided only that it transmits the unmodulated carrier as well as at least one modulated side band. The modulator disclosed is of the type disclosed; in U. S. patent to Van der B111 No. 1,350,752, issued Au 24, 1920. A modulator of the t e o M, in which the radio carrier would suppressed, could be used if the control radio carrier were independently transmitted.

Fig.2 illustrates the circuits at the controlled station for receiving and utlhzmg the control waves.

Such waves are received by auxiliary antenna AN, and demodulated in device D,. Since it is desired to utilize both of the carrier frequencies, a balanced demodulator like D cannot be used. Any other device capable of demodulating a modulated carrier wave may, however, be used. The one illustrated is of a conventional type identical in all respects to modulator M, except as to the values of the frequencies concerned.

The output of D, contains the control low and radio frequency carriers. The low frequency carrier is selected by tuned circuit 4 and impressed on harmomc producer 5H This harmonic producer may be ldentical with H, have the same function, and be related to the transmitting and receiving circuits at its station in the same manner. The radio frequency carrier is selected by tuned circuit 5 and impressed on harmonic producer H, to produce a radio frequency carrier wave having the same frequency as the radio carrier frequency at the master station. Harmonic producer H, is related to the transmitting and receiving circuits at the controlled station in the same manner as the harmonic producer H at the master station. fact. the transmitting and receiving clrcults at the controlled station may be identical with those at the master station except only that the tuned circuits 4 and 5 replace respectively carrier sources G and G It has been assumed that amplification accompanies harmonic production but it is understood that separate steps of am lification may be used if desired. Since only a very small amount of control ener is received, it is convenient to consider the armonic generators as local carrier sources, the frequenciesof which ar controlled by the control wave. 1

What is claimed is: i

1. The method of radio signaling between a master station and a controlled station which consists in generating a modulating wave at each station, generating a carrier frequency wave at the master station, producing a suppressed carrier modulated carrier wave at the master station from said waves, radiating said modulated wave,-deriving a control wave having a frequency which is commensurable with but different from that of said carrier wave, independently radiating said control wave, deriving a carrier wave at the'controlled station from said control wave and producing a su pressed carrier modulated carrier wave at t e controlled station from said derived carrier and a modulating wave produced at said controlled station. 4

2. The method of radio signaling between a master'station and a controlled station which consists, in generating a modulating wave at each station, generating a control wave at the master station,deriving a harmonic frequency wave from. said control wave, producing asuppressed carrier modulated carrier wave at the master station from said modulating and harmonic frequency waves, radiating said modulated wave, independently radiating said control wave, deriving a harmonic frequency wave at the controlled station from said control wave, and producing. a suppressed carrier modulated carrier wave at the controlled station from the modulating and harmonic waves at said controlled station.

3. The method of radio signaling between two stations which consists in transmitting suppressed carrier modulated carrier waves of the same carrier frequency from the two stations, and controlling the frequency of the carrier wave atone station by a control wave transmitted from the other station, said control wave being derived and transmitted independently of said modulated carrier harmonic carrier frequency control wave transmitted from the other station, said .control wave being derived and transmitted 1ndependently of said modulated carrier wave transmission.

5. The method-of radio signaling between a radio transmitting station and a radio receiving station which consists in transmitting a suppressed carrier modulated carrier wave from the transmitting station, combining the received wave at the receiving station with a locally produced carrier wave, and controlling the frequency of said locally produced carrier wave by a sub-harmonic carrier frequency control wave-transmitted from the transmitting station, said control wave being derived and transmitted independently of the modulated carrier wave transmission.

6. The method of radio signaling between two stations which comprises generating at and radiating from each station a doubly modulated carrier wave and controlling the a carrier frequencies at one station by anontrol wave transmitted from the other station independently of the doubly modulated wave transmissio 7. The method of radio signaling between twostations which comprises generating at and radiating from one station and demodulating at the other station a doubly modulated carrier wave in which the unmodulated low and radio carrier components are suppressed, transmitting from the first station a radio carrier control wave modulated by a low frequency control wave, and controlling the carrier frequencies used for demodulation by said control wave transmitted from the otherstation.

8. The method of two-way radio transmission between two stations which comprises generating at and radiating from each station a doubly modulated carrier wave, independently transmitting from one station a radio carrier control wave modulated by a low frequency carrier control wave, and controlling the carrier frequencies at the other station by said control wave.

9. The method of radio signaling between two stations which comprises generating a low frequency control wave, deriving as a harmonic thereof a .low frequency carrier wave, generating a modulating wave, producing a suppressed carrier modulated carrier wave from said modulating and low frequency carrier waves, generating a radio frequency control wave, deriving a harmonic frequency radio carrier wave therefrom, producing with said radio carrier wave and said modulated Wave a suppressed radio carrier modulated radio carrier wave, radiating said modulated radio carrier wave, modulating the radio frequency control wave in accordance with the low frequency control wave, independently radiating said modulated control'wave, demodulating the modulated radio frequency control wave at the other station to obtain the low frequency control and radio frequency carrier control waves, deriving from the control waves at said other station by harmonic generation a radio frequency carrier wave and a low frequency carrier wave having the same frequencies respectively as the carrier waves at the transmitting-station and using the two derived carrier waves at said other station for transmitting from that station to the transmitting station modulated waves similar to those transmitted from said transmitting station.

10. The method of radio signaling between a master station and a control station which consists in generating at the master station a low frequency carrier control. wave and a radio frequency carrier control wave, radiating the radio control wave modulated by the low frequency control wave to the controlledv station, demodulating said modulated Wave at the controlled-station to yield the low and radio'frequency carrier control waves, deriving from the low frequency carrier control Wave at each station one or more low frequency carrier waves, deriving from the radio frequency carrier control wave at each station by harmonic generation a radio carrier wave, the frequency of each low and radio frequency carrier 'wave at one station beingv identical with that of a corresponding carrier wave at theother station, modulating each of said low frequency carrier waves in accordance with a signal with the supipression of the carrier, modulating the radio requency carrier wave at each station in accordance with each of said modulated low fre uency carrier waves with the suppression o the radio carrier, radiating the resultant doubly modulated waves from each station, receiving at each station the waves transmitted from the opposite station, and obtaining the signals by combining said received waves with a portion of the local low and radio frequency carrier waves in two steps of demodulation.

11. A radio signaling system comprising in combination means at one station for generating and transmitting a suppressed carrier signal modulated wave, said means including a principal transmitting antenna, means at the other station for receiving and demodulating said wave including a local 7 carrier source, and an auxiliary antenna for separating and independently transmitting a wave from the transmitting station to control the frequency of the wave from said local source.

12. A radio signaling system comprising in combination means at a transmitting station for producing a suppressed carrier sig nal modulated wave, a transmitting antenna therefor, a receiving antenna at a cooperating receiving station, means at the receiving station for demodulating the received waves including a local carrier source, and means for transmitting a wave from the transmitting station forcontrolling the frequency of the wave from said local source, and for receiving it at the receiving station, said means ineluding a separate auxiliary antenna at each of the stations.

13. A one-way channel of a radio signaling system comprising, at a transmitting station, a'control frequency source, means for deriving a harmonic carrier frequency there from, means for generating therewith a suppressed 7 carrier signal modulated carrier wave, and a transmitting antenna, and, at the receiving station, a receiving antenna, a local carrier source, and means for combining the received wave with the wave from the local carrier source toproduce the signal, a

separate antenna at the transmitting station for transmitting control waves, a separate receiving antenna for receiving said control waves, and means whereby the received control waves determine the frequency of the local receiver carrier source.

14. A system like that recited in claim 13 including an additional similar one-way signal channel for transmission in the (:fposite' means having both carrier components suppressed,

a transmitting conductor, a receiving con ductor, and means utilizing said carrier sources for demodulating the receiving waves in two steps, and means for separately transmitting a wave from one station to control the frequencies of the carrier sources at the other station.

16. A radio signaling station comprising a carrier source, a source of modulating current, a'modulator, a selective circuit for suppressing one of the modulated side bands, a

common transmitting and receiving antenna, a selective circuit for receiving an incoming wave havin the opposite side band of the same carrier frequency as the transmitted wave, a demodulator for reproducing a modulating component from the modulated received waves, and means adapted to control the carrier frequency of the incoming waves without detriment to the efliciency inherent in a single side band transmission from said station.

17. A radio signaling station comprising acarrier source, a source of modulatin current, a balanced modulator for producing a suppressed carrier signal modulated carrier wave, a selective circuit for suppressing one of the modulated-side bands, a common transmitting and receiving antenna, a selective circuit for receivingan incoming wave having the opposite side band of the same carrier frequency as the transmitted wave, demodulating means for reproducin the modulatin component from the mo ulated receive waves, and means for controlling the carrier frequency of the incoming wave without affecting the efiicient transmission of said modulated carrier wave.

18. The method of two-way radio signaling comprising the steps of producing and transmitting in one direction a single side band of a doubly modulated wave, producing and transmittin in the other direction a similar single side and of'a doubly modulated wave, the oppositely directed transmissions having the same low and-radio carrier frequencies but opposite radio carrier side bands while conservm the eflicieney inherent in single side ban transmission.

19. The method of multiplex two-way radio signaling between two stations wh1 comprises, at each station, generating a control frequency wave, deriving a plurality of low frequency carrier waves as harmonics of said control frequency, modulating each of said low frequency carrier waves with a signal, suppressing at least one side band of each modulated wave and transmitting the remainin components including at least a side ban generating a second control wave, deriving a radio frequency carrier wave as a harmonic thereof, modulating said radio frequency carrier wave in accordance with said transmitted modulated waves, and'suppressing at least one side band of the radio frequency carrier wave and radiating the remainin components including at least a side ban modulating the second control Wave with the first control wave at'one station, independently radiating the resultant control wave, demodulating said resultant control wave at the other station, and controlling the frequencies of the low and radio equency carrier waves at said other station by. the demodulated com onents' of the received control wave, the ow and radio frequency carrier waves for one direction of transmission each being equal in frequency to corresponding carrier waves for the other direction, and opposite low and radio frequency carrier side bands being transmitted for the oppositely directed transmissions in each pair of transmissions having the same low frequency carriers.

20. A method of radio transmission of signals which consists in doubly modulating a carrier wave by first modulating signals on a relatively low frequency carrier and suppressing the unmodulated carrier so as to cave onl a side band, and then modulating this side and upon a high frequency carrier,

III

- and radiating the same, while simultaneously imposing an auxiliary unmodulated alternating current upon a. separate high fre quency carrier and radiating the same.

In Witness whereof, I hereunto subscribe my name this 22nd day of November, A. D.

v ROY E. CORAM. 

